Concavo-convex steel rule construction



Nov. 4, 1952 F. o. CARLSON CONCAVO-CONVEX STEEL RULE CONSTRUCTION Filed Sept. 10, 1949 II ||l lllllll llllll 50:0}

m w m ma 56 V. m C S v {NB C i m w F ATT Patented Nov. 4, 1952 CONCAVO-CONVEX STEEL RULE CONSTRUCTION Frederick 0. Carlson, Monrovia, Calif., assignor to Carlson & Sullivan, Inc., Monrovia, Calif., a corporation of California Application September 10, 1949, Serial No. 114,984

This invention relates to concavo-convex steel rule constructions and more particularly to a pocket-size casing of smaller over-all dimensions than has heretofore been commonly available containing a coiled concavo-convex steel rule measuring tape for general purposesillustratively of a six foot length. In the presently preferred form the invention is embodied in a case of molded plastic material the use of which in combination with other aspects of the invention contributes certain advantages. The casing, instead of being of standard .pillbox-shape exterior, incorporates a carefully configured nose portion which promotes easy readability of the tape at the point where the tape emerges from the casing and at the same time provides for certain built-in attributes as will be brought out hereinafter.

In the past, concavo-convex steel taperules of ordinary household size have commonly been supplied either in a casing of pillboX-shape exterior or in a casing having three straight sides at right angles to one another and a fourth semicylindrical side tangentially joining the ends of the two opposing straight sides. Neither shape has lent itself to a really small and compact rule unit.

I have devised a ruler and casing assembly having a smooth and easy action of'coiling and uncoiling which assembly facilitates direct readingof the withdrawn ruler and yet has an overall diameter not substantially in excess of 1.5

inch. Accordingly it is materially more compact and lighter in weight than the so-called pocketsize rulers heretofore available in six foot lengths.

It is an object of my invention to provide a concavo-convex pocket-size steel tape measuring rule assembly of the character described having to a notable extent the characteristics and capabilities set forth. A further objective is to provide a compact pocket-size rule assembly which overcomes certain of the disadvantages inherent in the constructions heretofore commonly known. A further objective resides in the provision of a steel tape ruler in combination with a casing of molded plastic material which combination affords an easy coiling action and which lends itself to incorporation in an assembly of minimum over-all configuration. A still further object'is to provide a concavo-convex steel ruler and casing'assembly which is easy to read in use and which incorporates certain advantageous built-in features. Other objects will in partbe pointed out as the description proceeds andwill in part become apparent therefrom.

The invention accordingly consists of the fea- 1 Claim. (Cl. 24284.9)

tures of construction, combinations of elements, methods of operation and arrangements of parts as will be exemplified in the structure and sequences and groups of related steps to be hereinafter described and the scope of the application of which will be set forth in the accompanying claim.

In this specification and the accompanying drawings I have shown and described a preferred embodiment of my invention and suggested various modifications thereof; but it is to be understood that these are not intended to be exhaustive nor limiting of the invention but, on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings:

Figure 1 shows a cross section through a casing containing a coiled ruler embodying my invention, the view being taken in a plane perpendicular to the winding axis;

Figure 2 is a view similar to that of Figure 1 but showing the relationship of parts assumed when the ruler is withdrawn from the casing;

Figure 3 is a cross-sectional plan view through the ruler and casing assembly taken in a plane containing the winding axis; and

Figure 4 is a fragmentary sectional view on an enlarged scale taken along the line 4@ of Figure 1 looking in the direction of the arrows.

As shown in Figure 3, the illustrative assembly embodying my invention includes aconcavo-convex steel tape ruler 26 having its inner end 2| attached to the outer end 22 of a windup spring 23 (see also Figures 1 and 2), the windup spring itself being contained within the complementary halves 24 and 26 which together form the casing generally indicated at 28. Casing half 24 includes as an integral part thereof a center post 39 and the casing halves 24 and 26 are heldin assembled relationship by a holding screw 32 passing through a central opening in casing half 28 and threaded into a hole 34 formed coaxially within post 30. l

As best shown in Figure 2, post 30 is provided with a slot 36 lying in a plane parallel tobut spaced from the axis of the post; the inner-end 38 of the windup' spring is secured within the slot 36.

Casing 28 is provided with'a nose generally indicated at dllwhich forms the housing-for an angled tape passageway 42 extending inwardly from a case opening 44 through which the withdrawable end of ruler 28 passes. Nose as includes a pair of side portions Alba and @527 formed in the casing which portions blend tangentially with the adjacent cylindrical portions of the casing as shown in Figures 1 and 2. Passageway 52 imposes a controlled braking action upon the ruler portion passing therethrough which action increases as the diameter of the windup spring decreases upon withdrawal of the tape and at a rate related to the increase in windup spring power as the spring is wound. This controlled braking action is a previous invention of mine and is described and claimed in my Patent No. 2,510,939 of June 6, 1950. Passageway 42 in addition acts as a close-fitting housing in which one leg 16 of tip piece 48 is disposed when the ruler is fully coiled within its casing. Leg 4B is riveted in conventional fashion in fiat face-to-face relationship upon the outer end of ruler 2d and the other 4 leg 58 of tip piece 58 projects downwardly, as shown in Figures 1 and 4, to provide a means readily accessible for withdrawing the end of the ruler from the casing upon demand.

shown in Figure 4, the cross section of passageway '62 adjacent opening 44 approximates the combined over-all cross section of the end of ruler is and leg it so that when leg 55 is pushed flush against the surface of nose id entrance ,44 and passageway '42 are substantially and eiiectively blocked. Thus dust and other small particles are precluded from gaining access to the interior of the casing.

An 'important'feature of my invention resides in the fact that I fashion the casing halves 2i.

and Y28 from moldings of suitable plastic material, such as .Ethocel, cellulose acetate, or the like.

The ruler itself is made of hardened steel and accordingly it is feasible to design the passageway so as to fit relatively accurately the portion of the ruler passing therethrough and thus to avoid any substantial clearance such as would be advisable if the casing were of a relatively hard drawn or die-cast metal. The plastic material is automatically ;maintained in a smooth,

quasi-lubricated condition by the polishing action of theruler as it passes in and out through the passageway but the polishing action in no way impairs the quality or long life of the steel tape.

As is well known, a transverse cross section through a concavo-convex steel ruler tape (as shown, for example, in Figure l) defines generally an arc of a certain radius of curvature. The smaller this radius of curvature the-smaller will be the natural coil which will be formed when the ruler is coiled with its concave side facing inwardly, as is customary, and thus the shorter this radius :of concavity the smaller the or coil a concavo-convex steel ruler it is necessaryto supply a sufficient bending force to overcome the inherent spring action of the ruler which normally causes the ruler to assume the concave-convex cross section. The smaller the radius of curvature of the concavo-convexity the greater the inherent spring action in the ruler and accordingly the greater the bending force necessary in order to retain the ruler, or a given length of ruler, in a. bent or coiled configuration.

I have found by experimentation with a metal thickness in the tape which forms the ruler of not over .007 inch, and with a tape width in the range of from to inch, and with a metal temper of the character generally desirable for giving the desired degree of stiffness and flexibility to the ruler, that a center post of a minimum over-all diameter of /4 inch is commercially possible. A smaller diameter than inch will result in crystallization of the metal which will impair the expected longevity of the ruler assembly and for a six foot ruler I have discovered that the minimum over-all diameter of a satisfactory windup spring mounted on a /4 inch center post cannot satisfactorily be must less than of an inch when tightly wound on the center post. I have further discovered with a six foot ruler fully coiled within a casing, and with a relaxed windup spring coiled within the coiled ruler, that the over-all diameter of the fully coiled ruler cannot be reduced satisfactorily much beyond 1.5 inch.

Accordingly, the interior diameter of casing 28 in the illustrative form is approximately 1.5 inch. From the foregoing relationships it will be observed in Figure 2 that the dimension A across the diameter of the center post is about .25 inch, that the dimension B across the tightly coiled diameter of the windup spring is about .75 inch, and that the dimension C across the interior diameter of the casing is about 1.5 inch. And in general, dimension B is three times dimension A, and dimension C is twice dimension B and six times dimension A.

I have further discovered that if the over-all angular dimension subtended by nose portion 46 is less than degrees the readability of the tape when withdrawn, as indicated in Figure 2, is enhanced. In the illustrative embodiment this over-all angle subtended by the nose is less than 90 degrees by .an amount measured on the drawings by angle D and in practice I have found it desirable that angle D be on the order of approximately 5 degrees.

From the foregoing it will be observed that a concave-convex steel tape measuring ruler assembly made in accordance with the present invention is well adapted to attain the ends and objects .hereinbefore .set forth and to be economically manufactured since both the article and the methods of making it aresuited to common production practices and are susceptible to a wide latitude of variations as may be desirable in adapting the invention to different applications.

As various embodiments may be made of the aboveinvention and aschanges might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be r interpreted as illustrative and not in a limiting sense.

I claim: A pocket-size steel ruler assembly of minimum over-all dimensions including: a substantially the outer end of Said windup spring and with its outer end passing through said ruler opening, and an L-shaped tip piece having one of its legs secured flat against the end of the ruler and the other of its legs extending at substantially a right angle therefrom and forming an abutment which prevents the outer end of the ruler from being drawn by the spring through the opening into the case; the interior of said case defining a substantially cylindrically shaped compartment, a nose forming a part of the case in the region of said opening and defining interiorly thereof a ruler passageway leadin substantially tangentially from said compartment to said opening, said passageway being not substantially longer than said one leg of said L-shaped piece and in cross section snugly fitting around said ruler and said one leg, said nose having a pair of exterior side portions blending substantially tangentially with the substantially cylindrical shape of said case and coming together in a dihedral- 6 like tip defining an angle of about 85 when viewed in profile looking parallel to the axis of the center post, said opening being located closelyl adjacent said tip, and said ruler having measuring indicia on its side facing away from the other portion of said nose.

FREDERICK O. CARLSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 578,205 Brown et al. Mar. 2', 1897 2,052,252 Stowell Aug. 25, 1936 2,129,582 Johansson Sept. 6, 1938 2,347,273 Lyle Apr. 25, 1944 2,446,020 Nicholson et a1 July 2'7, 1948 2,469,674 Witchger May 10, 1949 

